This invention relates to flextensional transducers and more particularly to a flextensional transducer in which hydrostatic pressure on the flexing portion of the transducer is coupled to the drive material so that the compressive stress originally introduced in the drive material at atmospheric pressure in a normal air environment is maintained or increased as the transducer is subjected to water pressure upon submergence.
In the prior art, the flextensional transducer 10 shown in the isometric view of FIG. 1 is comprised of a driver 11 which could be either a ceramic stack or magnetostrictive material each appropriately energized as known to those skilled in the art. A housing 12 comprising end portions 13 and flexing or shell portions 14 is arranged to provide compressional force on the driver 11 for reasons known to those skilled in the art. This compressive force is most commonly obtained by applying a transverse force to the shell portion 14 which elongates the separation between the ends 13. Insertion of the drive 11 between the elongated ends 13 is followed by release of the transverse force on the flexing sides 14 to result in a compressional force upon the drive 11. Alternatively, as is known to those skilled in the art, a threaded rod extending from one end 13 to the other end could be tensioned to provide a compression force upon the drive 11. The transducer is constructed with end panels not shown in FIG. 1 to provide a watertight enclosure generally containing air at atmospheric pressure when assembled. In operation, the transducer 10 is generally immersed in a substantial depth of water thereby creating inward pressure upon its shell portions 14 thereby reducing the compressional force being applied to the drive 11 in accordance with the depth of operation of the transducer. Therefore, the transducer design 10 of FIG. 1 is generally limited in its operating depth performance since a compressive force must always exist on the drive 11 to overcome the dynamic stresses induced by electromechanical drive.
Another prior art patent, U.S. Pat. No. 4,706,230, describes a structure which contains levers to magnify the expansion of the transduction material to obtain greater movement of the shell portions of the transducer. A rigid member supports the lever by acting as its fulcrum. Movement of the lever is accomplished by making its points of attachment to the transduction material, the shell, and the rigid member by connecting cantilevered members which flex or bend. The connecting members should have the conflicting desired properties of low bending stiffness with high longitudinal stiffness. Fatigue failure and noise generation are defects of the connecting members of this prior art patent. Water pressure-resisting properties of the transducer deteriorate if the strength of the connecting members is insufficient. When the strength is sufficient to resist the water pressure, the transducer acoustic performance is reduced because of the energy required to flex or bend the connecting members.